Field of Invention
The invention generally is related to the area of antennas, and more particularly related to integrated antenna arrays structured in a way and controlled electronically to form a desired antenna pattern without developing a null.
Related Art
An antenna system is an indispensable component in communication systems. In conventional wireless communications, a single antenna is used at the source, and another single antenna is used at the destination. This is called SISO (single input, single output). Such systems are vulnerable to problems caused by multipath effects. When an electromagnetic field (EM field) is met with obstructions such as hills, canyons, buildings, and utility wires, the wavefronts are scattered, and thus they take many paths to reach the destination. The late arrival of scattered portions of the signal causes problems such as fading, cut-out (cliff effect), and intermittent reception (picket fencing). In a digital communications system like the Internet, it can cause a reduction in data speed and an increase in the number of errors.
The use of smart antennas can reduce or eliminate the trouble caused by multipath wave propagation. A smart antenna is a digital wireless communications antenna system that takes advantage of diversity effect at the source (transmitter), the destination (receiver), or both. Diversity effect involves the transmission and/or reception of multiple radio frequency (RF) waves to increase data speed and reduce the error rate. Smart antennas (also known as adaptive array antennas, multiple antennas and, recently, MIMO) are antenna arrays with smart signal processing algorithms used to identify spatial signal signature such as the direction of arrival (DOA) of the signal, and use it to calculate beamforming vectors, to track and locate the antenna beam on a mobile target.
Most of the smart antennas in use today have some undesired nulls in the antenna patterns. In radio electronics, a null is an area or vector in an antenna radiation pattern where the signal cancels out almost entirely. If not carefully planned, nulls can unintentionally prevent reception of a signal and fail to transmit a signal. There is a need for an antenna system that has a controllable antenna pattern without developing nulls.